Metal-catalyzed cyclopropanation of olefins with diazo reagents has attracted great research interest because of its fundamental and practical importance. (Lebel et al., Chem. Rev. 2003, 103, 977; Davies H. M. L., Antoulinakis E., Org. React. 2001, 57, 1; Doyle M. P., Forbes D. C., Chem. Rev. 1998, 98, 911; and Padwa A., Krumpe K. E., Tetrahedron 1992, 48, 5385-5453.) The resulting cyclopropyl units are recurrent motifs in biologically important molecules and serve as versatile precursors in organic synthesis. (Pietruszka J., Chem. Rev. 2003, 103, 1051; Wessjohann et al., Chem. Rev. 2003, 103, 1625; Donaldson W. A., Tetrahedron 2001, 57, 8589; and Salaun J., Chem. Rev. 1989, 89, 1247.) In the past two decades, outstanding asymmetric catalytic processes, notably those based on copper, rhodium and ruthenium have been developed to allow for the synthesis of chiral cyclopropane derivatives from olefins with diazoacetates in high yields and high selectivities. (Fritschi et al., Agnew. Chem., Int. Ed. Engl. 1986, 25, 1005; Evans et al., J. Am. Chem. Soc. 1991, 113, 726; Lo et al., J. Am. Chem. Soc. 1998, 120, 10270; Maxwell et al., Organometallics 1992, 11, 645; Doyle et al., J. Am. Chem. Soc. 1993, 115, 9968; Davies et al., J. Am. Chem. Soc. 1996, 118, 6897; Nishiyama et al., J. Am. Chem. Soc. 1994, 116, 2223; and Che et al., J. Am. Chem. Soc. 2001, 123, 4119.)
While a number of catalytic systems worked exceptionally well with styrene derivatives and some electron-rich olefins, asymmetric cyclopropanation of electron-deficient olefins containing electron-withdrawing groups such as α,β-unsaturated carbonyl compounds and nitriles have proven to be a challenging problem presumably due to the electrophilic nature of the metal-carbene intermediates in the catalytic cycles. This catalytic asymmetric process would be highly desirable as the corresponding electrophilic cyclopropanes containing two or more electron-withdrawing groups have shown to be valuable synthetic intermediates for various applications. (Gnad F., Reiser O., Chem. Rev. 2003, 103, 1603; Cativiela C., Diaz-de-Villegas, M. D., Tetrahedron: Asy. 2000, 11, 645; Wong et al., Chem. Rev. 1989, 89, 165; and Danishefsky, Acc. Chem. Res. 1979, 12, 66.)
Among several previous efforts towards metal-catalyzed cyclopropanation of electron-deficient olefins with diazo reagents (Doyle et al., J. Org. Chem. 1980, 45, 1538; Doyle et al., J. Org. Chem. 1982, 47, 4059; Nakamura et al., J. Am. Chem. Soc. 1978, 100, 3443; Denmark et al., J. Org. Chem. 1997, 62, 3375), the most notable example is the (Salen)Ru-based asymmetric catalytic system recently reported by Nguyen and coworkers (Miller et al., Angew. Chem., Int. Ed. 2002, 41, 2953; and Miller et al., Angew. Chem., Int. Ed. 2005, 44, 3885). (For intramolecular asymmetric cyclopropanation of electron-deficient olefins, see: Lin W., Charette A. B., Adv. Synth. Catal. 2005, 347, 1547; for a Cu-catalyzed asymmetric [4+1] cycloaddition of α,β-unsaturated ketones with diazoacetates, see: Son S., Fu G. C., J. Am. Chem. Soc. 2007, 129, 1046; for an organocatalytic process, see: Papageorgiou et al., Agnew. Chem., Int. Ed. Engl. 2003, 42, 828.)
It was shown that methyl methacrylate could be effectively cyclopropanated with ethyl diazoacetate (EDA) using a 5:1 ratio of olefin:EDA, producing the desired product in high yield and high selectivities (both diastereoselectivity and enantioselectivity). However, only moderate results were obtained with acrylonitrile even when the reactions were run in neat olefin.